The invention relates to a process and device for sealing hard gelatin capsules and for packaging a dose of a liquid product in the thus sealed capsule, the sealing and packaging operations being able to be carried out automatically at high speed, with a production for one device of several capsules per second.
The use of envelopes generally made of gelatin, called capsules, is more and more widespread, particularly for packaging solid or liquid medicines. There can be distinguished at present capsules made from hard gelatin and more currently called by the simple term "gelules", and soft gelatin capsules designated more currently under the term "capsules", the first being used for packaging solid medicines, in granular or powder form, whereas the second are more particularly reserved for packing liquid medicines.
Hard gelatin capsules are formed from two distinct parts, namely the "cap" and the "body" fitting one into the other so as to form the complete capsule. The cap and the body are manufactured by the same process consisting in immersing in a gelatin solution the end of a mandrel whose form corresponds to the inner volume of the cap or of the body, then in withdrawing the mandrel from the solution and in letting the layer of gelatin thus deposited dry, which is then removed like a glove finger. In practice a large number of mandrels are used simultaneously transported by a conveyor which ensures successively the immersion of the end of the mandrels, then their passage through a drier, which enables very high production rates per unit of time to be attained.
Soft gelatin capsules are manufactured by a quite different process, which consists in passing between two cylinders having parallel axes and being provided with pockets, two strips of soft gelatin between which is located the product to be packed, which is in principle in liquid form. In the vicinity of the plane containing the axes of the cylinders, the two gelatin strips are highly compressed between the surfaces, at that time very close to one another, of the two cylinders, so that the liquid product to be packed is pushed back between the two gelatin strips to the position of the pockets provided in the cylinders and that, on the other hand, the two gelatin strips are welded together around the periphery of these pockets under the pressure exerted thereon by the cylinders. The sealed capsules thus formed and containing the liquid product are then removed from the gelatin strips. This process also allows very high rates to be obtained but it is much less economic as far as the use of the gelatin is concerned than the dipping process used for manufacturing hard capsules, for the part of the soft gelatin strips situated between the capsules are lost. Apart from this very high outlay for gelatin, another disadvantage of the soft capsule with respect to the hard capsules is that the product must, as we have just seen, be of necessity packed at the same time as manufacture of the envelope of the capsule and on the same installation. This poses difficult problems for, in a general way, the batches of medicines to be packed correspond to a relatively small number of capsules if we compare it with the capacity of production of the installation for manufacturing the capsules. It follows that this installation must be frequently stopped and cleaned to go over from one batch of medicine of a given formula to another batch of another formula. These frequent stops lower considerably the average production rate of the installation, which added to the higher outlay for material further increases the price for packing into soft capsules. On the other hand, in the case of hard capsules where the manufacture of the envelope of the capsule and the packing operations are carried out on separate installations, installations may be provided for packaging whose operating rates are adapted to the size of the series to be treated, so that these installations operate at full capacity and that this, added to the economy achieved for the material, allows the price for packing into hard capsules to be maintained at as low a level as possible.
As furthermore, in numerous cases, it would be preferable to administer the medicine in liquid form rather than in a less directly assimilable solid form, it is clear that the possibility of using hard capsules, not only for packing the medicine in powdery or granular form as is the case at present, but also in liquid form, would present the greatest interest. But the problem is particularly difficult for, since gelatin is a material likely to change from the dimensional point of view, it is necessary to provide during manufacture of the caps and bodies for hard capsules, considerable diametrical clearance so as to allow the cap to be fitted without difficulty onto the body. So that the cap after fitting on, despite this considerable clearance, does not separate from the body during handling to which the capsule will be necessarily subjected, so-called "snap-fit" devices are provided formed for example by an annular depression on the body corresponding with an annular inwardly directed bead on the cap, the interpenetration of the depression and the bead during fitting of the cap on the body holding these two parts of the capsule together. This snap fit which provides a certain locking effect between the cap and the body does not however remedy the lack of sealing of the whole due to the considerable play which it is necessary to provide between these two parts so as to allow fitting together.
Among the numerous attempts which have been made for sealing hard capsules and using them for packing liquid products, the following in particular can be mentioned:
Attempts have been made to form a sealed joint between the cap and the body by coating the outside of the hard capsule after fitting together with an adhesive which, after drying, will form a sealing film. But, apart from the fact that it is difficult to give to this film sufficient thickness for forming a sealed junction between the cap and the body, considering the considerable diametrical play existing at the junction between these two parts, drying of such an adhesive layer is particularly long and presents difficult problems due to the fact that as long as this drying is not completely finished the capsules cannot come into contact with each other.
Another attempt consisted in coating with a viscous adhesive the outer part of the body of the hard capsule which penetrates, on fitting together, into the cap. But the drawback is that, during fitting together, a part of this adhesive is pushed by the cap to the lower part of the body of the capsule, where it forms a bead and where it also presents a drying problem which is extremely difficult to resolve.
Attempts have also been made to incorporate in the liquid medicine intended to be packed in the capsule, additives giving it a thixotropic nature, so that this medicine acquires, after having been thus packed in the capsule, sufficiently high viscosity so as not to flow out through the clearance existing between the cap and the body and may, nevertheless, on arriving in the stomach where it will be subjected to certain mixing, assume again sufficient fluidity. But, besides the fact that the additives thus incorporated in the liquid medicine must be of such a nature and be used in such a quantity that this additive proves in numerous cases to be inadmissible and in others harmful, experience shows that results are not satisfactory. In fact, the thixotropic state of the product is unstable, particularly because of the vibrations to which the capsules are subjected during handling and transport, and after a certain time, leaks appear (all these techniques are described in particular in French Pat. Nos. 2 007 452, 2 385 389, 2 390 946, 2 390 948, 2 390 949 and in U.S. Pat. No. 3,078,629).